package com.ctgu.蓝桥杯真题.B组2015;

import java.util.Scanner;

/**
 * @author: Backdiy
 * @data: 2021/4/15 19:58
 * @desc:
 */
public class 饮料换购8 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n =scanner.nextInt();
        int ans=0;
        while (n>=3){
            n-=2;
            ans+=3;
        }
        ans+=n;
        System.out.println(ans);
    }
}
